A positive pressure unit (PPU) is a device used in healthcare to maintain a clean and safe environment, especially in rooms where patients with weakened immune systems are treated. PPU works by pumping clean air into a room at a higher pressure than the surrounding areas. This prevents contaminated air from entering the room, reducing the risk of infections spreading to patients. It creates a kind of protective bubble around the room, ensuring that only clean air flows inside and keeping harmful particles or germs out.